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>  News Releases >   2004 >   August

Dartmouth researcher sheds light on solar wind mystery

Posted 08/16/04

A new discovery brings scientists closer to understanding how high-energy particles from the sun - called the solar wind - are able to gain access into the earth's magnetic field.

Hiroshi Hasegawa
Hiroshi Hasegawa (photo by Mark Washburn)

Hiroshi Hasegawa, Research Associate at the Thayer School of Engineering, along with an international team of colleagues, has for the first time observed space vortices, much like curled ocean waves, that trap plasma and energy from the solar wind in the earth's magnetic field. The finding, published in the Aug. 12 issue of Nature, may help solve the 17-year-mystery of how the earth's magnetic field lets in the solar plasma when it should be acting as a barrier.

"These vortices were really huge structures, about six earth radii across," says Hasegawa, who has been analyzing the data collected by Cluster - a mission of four spacecraft launched on two Russian rockets during the summer of 2000. These satellites are now flying in formation around the earth, relaying the most detailed ever information about how the solar wind affects our planet.

Space physicists and engineers are striving to understand the exact mechanisms by which the solar wind enters earth's magnetosphere (the region in space where the earth's magnetic field dominates and interacts with the solar wind), because it forms the basis of space weather phenomena. These phenomena include the northern lights, radiation hazards for astronauts, satellites, and high-flying aircraft, as well as geomagnetic storms that can play havoc with technology on the ground and in space. These storms have been known to disable communication satellites, disrupt radio communications and radar detection systems, and create strong electric surges in power transmission lines, telephone wires, and even in pipelines, causing them to corrode.

The newly discovered vortices are known as products of Kelvin-Helmholtz instabilities.

"This is the first time rolled-up Kelvin-Helmholtz vortices have been detected unambiguously," said Hasegawa. "Past observations, which were based on single-spacecraft measurements, could not tell with certainty whether the waves along the edge of the magnetosphere were large rolled-up vortices or only small ripples that do not trap the solar wind."

"These multi-point, high time-resolution observations open a new window into understanding the connection of the solar wind to the earth's magnetosphere," said William Peterson, NASA's geospace program scientist.

The four Cluster satellites, built by the European Space Agency with participation from NASA, investigate three-dimensional structures throughout the earth's magnetosphere and solar wind. NASA supports U.S.-based researchers, including Hasegawa, who are associated with the mission.

The ongoing archiving of the Cluster data is part of the International Living with a Star program (ILWS), in which space agencies worldwide get together to investigate how variations in the sun affect the environment of earth and the other planets. In particular, ILWS concentrates on those aspects of the sun-earth system that may affect society. ILWS is a collaborative initiative between Europe, the United States, Russia, Japan and Canada.

By Catharine Lamm

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